Smart thinking by the US Air pilots. They realized something wasnt right. Probably heard it in United's voice. Was smart of them to slow everything down and get it figured out. If you do a little digging on that one you'll find a clip thats a little longer and controller is actually pretty ticked about the United flight and seems oblivious that there was a runway incursion and near miss. You can hear the other aircraft go past United on the radio they were so close. Scary stuff.

The atlas/united one happened at Ohare. It was a big story when it happened. Basically there were two tower controllers, one controlling the United runway(and parallel) and another the Atlas (and parallel). The united controller couldn't see the Atlas for whatever reason (think the other controller blocked his view) and issued the takeoff clearance.

I'll try and find a link to the other audio I mentioned earlier. It has a 3d rendering of the events as well. Of the Providence incursion. Scary stuff. But again the accident chain was broken when US Air refused the take off clearance until he thought it was safe.

OK here it is guys. 8 minutes worth. With a grainy animation. But you get to hear a little more of the aftermath of what happened after US Air refused takeoff clearance. You'll see at about 3:25 into the animation how close the Fed EX flight was.